Most of motors currently applied to unmanned aerial vehicles are three-phase brushless direct current motors, which are controlled by means of electronic speed regulators.
At present, a motor is controlled by mainly using a six-beat type square wave speed regulator on the market. That is, a speed of the motor is regulated by a duty ratio of converting an input pulse width signal to a Pulse Width Modulation (PWM) signal. However, since six phase changes are present within an electric angle period and a current waveform is a square wave, a large torque pulsation will be generated. The large torque pulsation may cause vibration of a propeller of an aircraft (unmanned aerial vehicle), thereby causing a certain influence on a overall stability of the aircraft, and generating a large noise.
In addition, the motor is also controlled by using a vector control method. That is, a voltage vector is controlled to be continuously output within the electric angle period according to a rotor position, and an output current waveform is a sine wave, so that stable rotor output can be realized. However, if a universal vector control method that generally is a speed closed-loop control manner is directly applied to the aircraft, the following problems will be present.
One, because signals input from a flight controller to an electronic speed regulator are pulse width signals of 0% to 100%, the pulse width signal of 0% and the pulse width signal of 100% respectively correspond to a given lowest rotating speed and highest rotating speed respectively. When the highest rotating speed is set, output may not achieve the highest rotating speed due to gradual voltage reduction of a battery, so as to make the aircraft out of control.
Two, the flight controller will output changing pulse width signals when stabilizing an aircraft attitude. This may cause a rapid change of a given speed. And an output torque will rapidly change according to speed closed-loop control, thereby causing a strong jitter of an aircraft body and making the aircraft unable to stably run.